Investors in healthcare’s big IPO class of 2013 have seen some wild swings in share values since the debuts of dozens of new public companies. Hot trading in the Cambridge, MA-based companies Foundation Medicine and Epizyme pushed their peak prices above $40 for a time, followed by declines that sent the stocks swooning below their initial closing prices. Redwood City-based Relypsa’s shares roughly doubled in value in less than a month.